Honestly, I'm gonna push back on this one. You said "40-cent relay" like it's some dumb luck thing, but that's just what the fix cost, not what the diagnosis was worth. The real problem was that you skipped the cheap, boring checks and went straight for the expensive parts. I've seen guys swap $800 modules and still miss a dirty ground wire because they refused to spend 20 minutes with a multimeter. That relay wasn't the gotcha, your process was.

Ugh, that sucks, but a backup key isn't really a backup if it's the same pen you use every day, right? I just accept the loss and carry a cheap ballpoint for emergencies, keeps the good stuff safe at home.

Did you ever check if the shelf was actually square before it started wobbling? In my experience, a diagonal brace fixes a lot, but sometimes those brackets are holding up a bad install, not the weight. The wood might be doing the heavy lifting, but the real lesson is learning to cut and fit stuff yourself, which is worth way more than $80.